The leech segmental nervous system has eleven monoamine-containing neurons. Most are small interneurons except for the Retzius Cells which have peripheral axons. Two cell bodies in the lateral roots contain catecholamine and those within ganglia contain indoleamines (5-HT in the Retzius cells). These neurons are vitally and selectively stained with Neutral Red dye and can each be impaled with microelectrodes. We propose to study the membrane properties, synaptic and electronic interactions, and anatomy of this uniquely-identifiable population of amine-containing neurons. Standard electrophysiological recording techniques will be coupled with some pharmacological experiments to determine if amine neurons have any unique properties.